apjohnite

[Named after Apjohn, who analysed it. A mineral, placed by Dana under his Alum and Halo trichite groups. It occurs in white fibrous or asbestiform ma es at Lagoa Bay, in South Africa. Composition: Sulphuric acid, 32-97; alumina, 10.65; sesquioxide of manganese, 7.33; water, 48-15; sulphate of magnesia, 1.08 = 100. *a-plā'çe, *a-plā's, adv. [Eng. a; place.] In one's place, before all. "Ther men anon forth a place hir brought, Fair melusine, enmyddes the chapel. The Romans of Partenay (ed. Skeat), 932-8 ăp-lăn-at-ic, a. [From Gr. a, priv., and πλανάω (plan aō) = to cause to wander; fro in πλάνη ( plane ) = wandering.] Not wandering; destitute of aberration. Aplanatic lens: One which, could it be constructed, would so refract all the rays of light incident upon it, whether they entered it in a direction parallel to its axis, or converged to, or diverged from, a point in that axis, as to make them all ultimately meet in a single point or focus. More than one form of lens would be aplanatic could it be made with mathematical exactne , different media being employed to render it achromatic. Lenses can at present be made only approximately aplanatic, and tables are therefore constructed to show how, with a given refractive index, the aberration of the focus may be reduced to a minimum. [ABERRATION, ACHROMATIC.]